Prospects of the organic electroluminescence (EL) device in which organic materials are used are promising as a solid luminescent type inexpensive and large area full color display device and development has been tried variously. An organic light emitting device in general comprises a luminescent layer and a pair of counter electrodes with the luminescent layer between. When an electric field is impressed between both electrodes, electrons are injected from the cathode and positive holes are injected from the anode, and the electrons and the positive holes are recombined in the luminescent layer. A phenomenon of emitting energy as light when energy level is returned from conduction band to valence band is luminescence (light emitting).
Organic light emitting devices so far been used require high driving voltage and emission luminance and luminous efficacy are low, but an organic EL device (element) comprising lamination of thin layers containing an organic compound having high fluorescent quantum efficiency capable of emitting light with low voltage of 10 V or lower has been reported (Applied Physics Letters, Vol. 51, p. 913 (1987)) and attracting public attention in recent years. According to this technique, high luminance green light emission can be obtained by using a metal chelate complex as the electron-transporting layer, a fluorescent compound as the luminescent layer and an amine compound as the positive hole-transporting layer. Further, when taking into consideration the utilization of an organic light emitting device as a full color display and a light source, it is necessary to get three primary colors or a white color in practical use. A device capable of emitting a desired color by doping a fluorescent dye is reported (Journal of Applied Physics, Vol. 65, p. 3610 (1989)). This technique is particularly effective for red luminescence in which extinction due to concentration is large and the emission of high efficacy is difficult when a fluorescent dye is used alone as the luminescent layer, and high color purity and high luminance have been attained due to the technique. However, when a device doped with a dye is produced by deposition, the operation is complicated and the performance of the device is liable to become uneven because a host material and a trace amount of a fluorescent dye are co-deposited. Therefore, from the viewpoint of the simplification of the producing step and the stability of the performance of a device, the development of light emitting materials having good color purity and capable of using a dye alone as the luminescent layer, in particular, light emitting materials of from red to green capable of attaining good chromaticity and luminance and excellent in durability even when a dye is used alone as the luminescent layer has so far been desired.
On the other hand, organic EL devices which have realized high luminance emission are laminated devices formed by vacuum deposition of organic materials, but from the viewpoint of simplification of producing step, processability, and realization of large area devices, it is desired to produce devices by a coating system. However, devices produced by a coating system so far been used are inferior to devices produced by a deposition system in the points of emission luminance and luminous efficacy, therefore, the realizations of high luminance and high efficacy light emitting have been left as the problems to be solved. In addition, with devices produced by coating an organic low molecular weight compound dispersed in an organic polymer medium, uniform planar emission for a long period of time is difficult due to the agglomeration of the organic low molecular weight compound.
Further, in recent years, various materials having fluorescence have been used for a filter dye, a color conversion filter, a dye for a photographic material, a sensitizing dye, a dye for pulp-dyeing, a laser dye, a fluorescent medicine for a medical diagnosis, a material for an organic light emitting device, etc., and demand for such materials has been increased. However, fluorescent dyes having high fluorescent strength and high color purity are less, therefore, the development of a novel material has been desired.